Biosensors are devices that use biochemical reactions to identify and detect various molecules and biochemical analytes. Biosensors are widely used in different life-science applications, ranging from environmental monitoring and basic life science research to Point-of-Care (PoC) in-vitro molecular diagnostics. Biosensors are known to be very sensitive and also extremely versatile in terms of detection as they can detect a small number of almost any kind of analyte, once a proper recognition molecule is identified. Example analytes that have been detected using biosensors include DNA and RNA strands, proteins, metabolites, toxins, micro-organisms, and even explosives molecules.
All biosensors, independent of the analyte they are trying to detect, include two key building blocks. One is the molecular recognition layer which is responsible for identifying and/or interacting with and/or reacting with and/or capturing the specific target analyte from the sample. The other is the sensor apparatus that detects and/or quantifies the interactions of the recognition layer with the analyte and provides a measurable output signal, generally in the form of an electrical signal. The molecular recognition layer typically comprises of carefully engineered and surface-assembled bio-molecules in the form of spotted or synthesized DNA oligonucleotides, aptamers, and antibodies attached to solid substrates, such as glass slides, micro-beads, electrodes, semiconductor materials, or dense polymers while the sensor includes optical-, MEMS- and/or electronics-based transducers connected to a low-noise detection circuit.
So far, there have been many detection methods that have been adopted in biosensor systems. A detection method is defined as the specific type of physiochemical mechanism designed into the molecular recognition layer, analytes, and the interaction environments that make the identification of the specific target analytes possible by the sensor. The most widely used detection methods are different classes of optical (e.g., fluorescence, bioluminescence) and electro-analytical (e.g., potentiometric, amperometric, impedimetric). It is also common to classify biosensors based on their detection method. For example, in bioluminescence-based biosensors, the interaction of the analyte and probes results in a bioluminescence phenomenon which is detected by a specific sensor with a transducer sensitive to bioluminescence signals.
Electro-analytical biosensors detect analytes by monitoring different electronic changes in electrode-electrolyte transducers that are specifically interfaced with a recognition layer. For instance, in amperometric biosensors, low-frequency Faradaic reduction-oxidation (redox) currents are used as an indicator for analyte interactions with the recognition layer, whereas in impedimetric biosensors, the changes in the electrode-electrolyte impedance induced by the captured analyte are used as an indicator of analyte interactions with the recognition layer.
Unfortunately, the existing state-of-the-art electro-analytical biosensors are not compatible with semiconductor Very Large Scale Integration (VLSI) manufacturing processes thereby not being able to take advantage of the VLSI processes (e.g., highest level of integration, miniaturization, cost-efficiency, and robustness).